Device for Removing Dirt and Short Fibers from a Fibrous Material

ABSTRACT

The invention relates to a method and a device for separating dirt and short fibers from a fiber material ( 42 ) in a preparatory machine for of a spinning apparatus. A conveying means ( 40 ) retains the fiber material ( 42 ) that is made up of a plurality of fibers. The device comprises at least one pair of electrodes ( 43, 44, 50, 51, 60, 61, 70, 71 ), and the pair of electrodes ( 43, 44, 50, 51, 60, 61, 70, 71 ) is connected to a source of high voltage ( 48 ) for the purpose of generating an electrical field having a field strength of (Ē). The pair of electrodes ( 43, 44, 50, 51, 60, 61, 70, 71 ) is disposed such that it is directed toward the fiber material ( 42 ), and the fiber material ( 42 ) is being moved in relation to the pair of electrodes ( 43, 44, 50, 51, 60, 61, 70, 71 ).

The invention relates to a preparatory machine for a spinning apparatus for separating dirt and short fibers from the fiber material.

The prior art discloses various devices for separating dirt and short fibers in preparation of the spinning operation. By way of a representative example, the problem will be described below in connection with cotton processing. In cotton processing, following cleaning and opening of the cotton fibers in order to obtain fiber flocks in the so-called blowing room, the cotton fibers are worked up and parallelized in a card. The fiber flocks are supplied to a taker-in via a feed chute, and the taker-in transfers the fibers to the card cylinder. The fibers are carded during multiple revolutions of the card cylinder, meaning the fibers are parallelized and aligned. So-called cards, which are in form of fixed or revolving flats, are disposed opposite of the card cylinder for this process. Clothings are disposed on the cards that cooperate with the clothings present on the card cylinder. This cooperation results in the longitudinal orientation of the fibers.

The context for the operation of a carding process according to the prior art is presently described in an exemplary manner based on FIG. 2:

FIG. 2 shows a schematic view of a representation of a carding process between a cylinder clothing 20 and a revolving flat 10 with a flexible clothing 21. The direction of rotation of the card cylinder, and thereby the moving direction 25 of the fiber material 22 that is retained by the cylinder clothing 20 is indicated by the arrow 25. The revolving flat 10 is moved in the direction 23. When the movement 23 of the revolving flat 10 occurs in the same direction as the card cylinder, it should be noted that the cylinder clothing 20 is moved much faster than the flexible clothing 21, wherefore the moving direction 23 of the revolving flat 10 is immaterial for the explanations. The fiber material 22 that is received by the cylinder clothing 20 is guided past the revolving flat 10, respectively the flexible clothing 21. Due to the friction between the clothing 21 and the fiber material 22, individual fibers initially get caught in the needle tips. Said needle tips serve as auxiliary means for capturing disturbing particles, such as parts of leaves 26, dust particles 27, parts of stems 28, parts of shells 29 and fiber neps 30. Any clogging of the clothing 21 is dependent, among other factors, on the configuration of the clothing 21.

The revolving flats basically fulfill four functions: they are provided to disintegrate the fiber flakes down to the individual fibers, separate out disturbing particles, dissolve fiber neps and parallelize as well as orient the fibers. Due to the fact that, as described above, a separation of dirt particles does not occur until after the individual fibers have been received, minimally contaminated raw materials require a reduced receiving action with regard to the individual fibers. The receiving of individual fibers, on the other hand, depends on the position of the clothings in relation to each other and on the configuration of said clothings. Moreover, the longitudinal orientation of the fibers is substantially influenced by the spacing between the clothings, the so-called carding gap.

Said carding method according to the prior art suffers from the disadvantage that any simultaneous cleaning and longitudinal aligning action of the fibers represents a compromise with regard to the requirements of both processes. Due to improvements with regard to cotton cleaning in the blowing room and higher performance outputs overall in cotton processing, the requirements that are demanded of the quality of the carding process have also continually increased. The use of high-performance cards, which are available today, along with improvements inside the blowing room facilities have resulted in the consequence that, today, excess fiber damage in relation to the achieved separation of dirt has become an unavoidable trade-off. For example, a high dirt separation rate on revolving flats has the disadvantage that the carding action must be deep, which means a great many of the material fibers are taken up inside the clothing and removed from the carding process in order to achieve a high level of dirt separation.

Therefore, it is the object of the present invention to provide a device that will allow for separating dirt and short fibers from the fiber material without causing damage to the fiber material or a loss of material fibers.

This object is achieved with the characteristics of the independent claims.

The object is achieved by a method for separating dirt and short fibers from a fiber material inside a preparatory machine for a spinning apparatus, wherein the fiber material is transported by a conveying means in a conveying direction. The fiber material is moved past at least one pair of electrodes that is connected to a source of high voltage, wherein an electrical field is generated between the electrodes of the pair of electrodes that is directed toward the fiber material, and field lines of the electrical field extend in a plane having an identical orientation in relation to the surface of the fiber material.

The object is also achieved by a device for separating dirt and short fibers from a fiber material inside a preparatory machine for a spinning apparatus, wherein the fiber material, which is made up of a plurality of fibers, is retained by a conveying means. The device comprises at least one pair of electrodes, and the pair of electrodes is connected to a source of high voltage for generating an electrical field having a field strength (Ē) and wherein the pair of electrodes is disposed such that it is directed toward the fiber material, and the fiber material moves relative to the pair of electrodes.

The science of electrical engineering teaches that different forces inside an electrical field can act on a so-called dielectric. A dielectric is essentially a non-conducting particle. Dirt and short fibers in a fiber material act like a dielectric inside an electrical field. In particular those forces are of interest that, when cleaning the fiber material, act on a dielectric perpendicularly in relation to the field lines of an electrical field. An electrical field can be generated between to capacitor plates, for example. The science of electrical engineering then teaches further that a dielectric is pulled between the capacitor plates and into the field, perpendicularly relative to the field lines. The tensile stress that is in effect on the dielectric perpendicularly relative to the electrical field lines (force per cross-sectional area of the dielectric, parallel in relation to the field lines that the dielectric pulls into the electrical field) is proportionate to the square of the field strength. The tensile stress is all the much greater, the higher the field strength, wherein the field strength corresponds to the quotient of the electrical voltage and the spacing between the capacitor plates. The field strength, and thereby the tensile stress on the dielectric, can be intensified by increasing the voltage and/or reducing the spacing between the capacitor plates.

The invention exploits these regularities as established by the electrical engineering field. A fiber material that must be cleaned is moved past a corresponding electrical field, wherein the individual components of the fiber material are attracted, by a certain tensile stress, by the electrical field. The electrical field is generated between two electrodes that are directed toward the fiber material. The electrodes therein have the identical function as the capacitor plates in the aforementioned example. The electrodes are connected to a source of high voltage to achieve a field strength in the field between the electrodes, which is a great a possible. The fiber material that must be cleaned is moved past the electrodes by a suitable conveying means. The conveying means is configured such that the so-called fibers of the fiber material are retained by the conveying means. This is achieved, for example, by providing correspondingly suited clothings or other types of adherion means. The arrangement of the electrodes is achieved in such a manner that the field lines of the electrical field, which has been generated between the two electrodes, run inside a plane that is identically aligned with the surface of the fiber material. Ideally, the field lines extend in a plane that is parallel in relation to the surface of the fiber material; this way, the maximum possible force would be in effect on the individual components of the fiber material. However, a course that is aligned is sufficient to achieve the desired effect. Same alignment therein is understood to mean that a plane, where the field lines are located, is not inclined by more than 60° relative to the surface of the fiber material. If the incline is 60°, the orthogonally acting force, which is in effect on the surface of the fiber material, drops by 50%. Experiments have shown that already at 50% of the maximally possible action of force, it is possible to achieve a good cleaning effect. This means that the surfaces of the electrodes are directed toward the fiber material with regard to the orthogonal, relative to the surface of the fiber material that is to be cleaned, even when they are at an angle of +60° to −60°. An alignment of the electrical field relative to the conveying direction of the fiber material is not necessary, on the other hand, because the determinative action of force of the electrical field occurs orthogonally in relation to the field lines.

For a better understanding, the possible arrangement of the electrodes for achieving the desired effect of the electrical field, which is generated between two adjacent electrodes, will be described below using the vectors that indicate the field strength. The fiber material is conveyed past the electrodes at a certain speed. Based on this, it is possible to define a speed vector at the location of the surface of the fiber material. The speed vector must be applied to each location of the fiber material. For example, if the fiber material is conveyed using a cylinder, this will, consequentially, result in speed vectors that are applied tangentially to the envelope curve of the cylinder. The field strength vectors are directed, at each location of the electrical field, in the direction of the field lines. At the point where the field lines exit from the electrode, the corresponding field strength vector is arranged orthogonally in relation to the surface of the electrode. When the surfaces of adjacent electrodes are not disposed parallel in relation to each other, the field strength vector of a field line follows as a resultant from the vectors of the field strength applied at each point on this field line. Said resulting field strength vector is located inside a plane that has the same alignment in relation to the plane that is created by the speed vectors. Same alignment must be understood to mean that the two planes do not deviate by more than 60° from a parallel arrangement. The arrangement of the electrodes is such that a vector of the field strength is disposed having the same alignment in relation to a plane that contains the speed vector of the fiber material.

In contrast to the methods for cleaning fiber material that are known from the prior art, there occurs presently a deflection of the dirt particles and the short fibers without the fiber material coming into contact with the electrodes. According to known cleaning processes, the fiber material is beaten, combed and brushed. However, all of these methods cause great stress on the fiber material, while the same is undergoing the cleaning process. Contrary to this method, the proposed method is virtually touchless, whereby, while cleaning, the method protects the fibers that are transported by the conveying means, in as far as this is possible, against fiber damage. Moreover, there is a clear process-related separation between a cleaning step and the actual carding and/or parallelizing step, as well as the conveying step of the fiber material. It is no longer necessary to take up any fibers of the fiber material in order to achieve a high-level cleaning effect.

To generate an electrical field, the pairs of electrodes are connected to a source of high voltage. The high voltage is energized by means of a corresponding control and supplied to the pair of electrodes by means of electrical connections. High-voltage generators, or also capacitors, can be used as sources of high-voltage. It must be noted, however, that the connection between the source of high voltage and the pair of electrodes is to be configured such that the operator is shielded against the voltage. Also, the source of high voltage must be correspondingly connected to an energy source. If a high-voltage generator is used as a source of high voltage, a continuous energy supply must be ensured for the time period during which the electrical field is to be maintained between the electrodes. Contrary to this, the use of a capacitor has the advantage that the same can be charged by means of a connection to an energy source, whereafter it supplies the necessary high voltage for a certain amount of time thereafter in order to generate the electrical field without any requirement for having to maintain this connection. The electrical field can be generated solely with the stored energy in the capacitor.

Advantageously, the electrodes are configured as plates. The two plates on a pair of electrodes are disposed at a certain spacing relative to each other. The action of force, which is perpendicular in relation to the field lines, can thus be enhanced in that a field strength of the electrical field between the electrodes of the pair of electrodes increases when the spacing relative to the fiber material is widened. A field strength that increases together with the spacing relative to the fiber material can be achieved, for example, by the selection of the geometric shape of the electrodes. When the electrodes have a thickness that decreases in the direction toward the fiber material, there results a inhomogeneous field strength along to the course of the electrodes. A further option provides for arranging the electrodes in a slanted position in relation to each other. The electrodes of one pair of electrodes are disposed in an inclined position relative to each other, wherein the spacing between the electrodes increases in the direction toward the fiber material. Moreover, mixed forms are conceivable as well; for example, a first part of an electrode can have a tapered cross-section and a second part can have a continuous cross-section. In addition, it is also possible for an end of the electrodes, which is directed toward the fiber material, to be bent in relation to the further extension of the electrode. Targeted inhomogeneity pulls the impurities and short fibers further into the electrical field, into a free space with the greatest field strength.

The field lines of an electrical field enter and/or exit the electrodes perpendicularly, respectively, in relation to the surface of the electrodes. Adjusted to the geometric shape of the electrodes, this results, in various embodiments, in slightly curved field lines. Regarding the effect, however, this is not relevant. With a symmetrical arrangement of the electrodes, the action of the force that is determinative for the cleaning action, is oriented in the direction of the angle bisector from the entry and exit angles of the field lines. The plane is determined by the course of the resultant. The plane, inside which the field lines extend, is always perpendicular to the action of the force, which is the sum of all orthogonally acting forces between two electrodes in relation to the field lines.

The absolute field strength must be generated using high voltage that is below the breakdown voltage in the air. The breakdown voltage in air is, under normal climate conditions, in the order of magnitude of 3,200 volts per mm. The maximum voltage that can be applied to the pair of electrodes without causing a spark-over is determined, on the one hand, based on the spacing between the electrodes and, on the other hand, based on the spacing between the electrodes and the fiber material. Experience has shown that it is possible to reliably avoid spark-over using a voltage of below 3,000 volts per mm.

The dirt particles and short fibers that are not retained by the conveying means are pulled between the electrodes and held there-between by the action of force, orthogonally in relation to the field lines of the electrical field. The particles and short fibers are retained by a polarization of the particles inside the electrical field, which results in them being leaned against one of the two electrodes and becoming interlaced therein by a corresponding friction action. In addition, it is helpful when, the farther the distance to the fiber material, the greater the field strength, because, with increased field strength, the action of force also increases orthogonally in relation to the field lines. The polarization converts dirt particles into polarized dipoles. By the longer axis thereof, these dipoles are arranged along the field lines of the electrical field. Due to the fact that the dirt particles, as dipoles, are weakly conducting, interconnecting them in a chain-like manner results in serially arranged virtual capacitor circuits. The tiniest spacing between the dirt particles or parts of the surfaces thereof can result in locally elevated field strengths. Due to these locally increased field strengths, the dirt particles keep adhering to each other in the thus formed chain-like interconnection.

In contrast, suitable devices retain the fibers of the material on the conveying means, thereby withstanding the force of attraction of the electrical field.

Advantageously, the electrodes are spaced 0.1 mm to 5.0 mm from the fiber material. Preferably, the spacing is in a range between 0.3 mm to 2 mm. The selected spacing depends therein on the desired cleaning effect and the properties of the fiber material that must be cleaned. Provided the spacing between the electrodes corresponds at least to double the spacing between the electrodes and the fiber material, there results a high voltage value of 500 V to 15,000 V that must be applied.

Advantageously, a plurality of pairs of electrodes is used in a device for separating dirt and short fibers from the fiber material in a preparatory machine for a spinning apparatus. The pairs of electrodes therein are disposed as offset, behind one another and adjacent to one another, such that all parts of the fiber material are transported past at least one pair of electrodes. It must be noted therein that, to the extent that this is possible, the total width of the conveying means is covered with pairs of electrodes, transversely in relation to the conveying direction of the fiber material.

Advantageously, the conveying means is a cylinder that includes a clothing as a retention means for the fiber material. The fibers of the fiber material are retained by the clothing of the cylinder, while impurities and short fibers are pulled into the electrical field. The rotation of the cylinder moves the fiber material, that must be cleaned, past the electrical field that is arranged radially thereto. Other facilities are also conceivable as conveying means, such as, for example, a conveying belt or a spiked lattice.

By collecting impurities and short fibers in the electrical field, said materials take up the space between the electrodes. To be able to keep the space between the electrodes free, it is possible to provide for a cleaning device, which is be used to keep the space between the electrodes of a pair of electrodes unclogged. Embodiments of such a cleaning device are known from the prior art. For example, the space can be continuously or periodically freed of impurities and short fibers by applying suction. Or, in support, it is also possible to move the pairs of electrodes from the operating position to a maintenance position thereof. This can be achieved by extending or pivoting the pairs of electrodes. Correspondingly, the pairs of electrodes are mounted on a suitable carrier means.

The invention will be described in further detail below based on the figures. Shown are as follows:

FIG. 1 is a schematically simplified view of a representation of a revolving flat card according to the prior art;

FIG. 2 is a schematic view of a representation of a carding process according to the prior art between a cylinder clothing and a flexible clothing;

FIG. 3 is a schematic view of a representation of a first embodiment;

FIG. 4 is a schematic view of a representation of a second embodiment;

FIG. 5 is a schematic view of a representation of a third embodiment;

FIG. 6 is a schematic view of a representation of a fourth embodiment;

FIG. 7 is a schematic view of a representation of a fifth embodiment.

FIG. 1 shows a common arrangement of a card according to the current prior art, particularly a card 1 with a filling chute 2 disposed upstream thereof. The fiber material is transferred to the taker-in 3 via the filling chute 2 in form of fiber flakes; the taker-in, in turn, forwards the fiber material to the card cylinder 4. A revolving flat set 5 is disposed above the card cylinder 4. The revolving flats 10 therein are moved over the surface of the card cylinder by means of a chain or belt and around the deflection pulleys 6. Depending on the configuration, the revolving flats 10 are able to move contrary to the direction of rotation or with the direction of rotation of the card cylinder 4. The carding work is performed by the revolving flats 10, for the most part. The doffer 7 removes the fibers, which have been aligned by the carding operation, from the card cylinder 4 and supplies them to a sliver means 8. The sliver means 8 combines the doffed web into a card sliver 9, transporting the same to the next machinery unit, for example a sliver deposit or line (not shown). A card is one of the different pieces of cleaning machinery that are used in the preparation of the spinning operation. In addition to being used in conjunction with a card, the device according to the invention is also suitable for use in so-called coarse cleaners or fine cleaners, as well as mixers, capacitors or lines.

A plurality of revolving flats 10 is provided on the mentioned revolving flat set 5, wherein FIG. 1 only provides a schematic view of individual revolving flats 10. Revolving flat sets 5 that are in use today comprise multiple, narrowly spaced revolving flats 10 that move circumferentially. To this end, the revolving flats 10 are supported in proximity of the respective frontal sides thereof by continuous belts, and they move against or with the direction of rotation of the card cylinder 4, and they are moved past the surface of the card cylinder 4 on the bottom side of the revolving flat set 5.

FIG. 2 shows a schematic view of a representation of the carding process according to the prior art, occurring between a cylinder clothing and a flexible clothing. The description of FIG. 2 is provided by the prior art.

FIGS. 3 and 4 show a schematic view of a representation of a first and a second embodiment. The fiber material 42 is conveyed by a conveying means 40 in the direction of movement 41. The conveying means 40 is represented, in an exemplary manner, as a clothing. A first electrode 43 and a second electrode 44 are disposed above the fiber material 42 with a spacing B there-between. The electrodes 43 and 44 are directed toward each other at a spacing A and constitute a pair of electrodes. The electrodes 43, 44 are depicted as plates; however, other geometrical forms are conceivable as well, for example pins. The electrodes 43, 44 are connected to a source of high voltage 48. This way, an electrical field is generated between the electrodes 43, 44, which is characterized by the field lines 47 and field strength Ē in the drawing. The field strength results from the quotient of the voltage that is applied by the source of high voltage and the spacing A of the electrodes 43, 44.

An action of force 45 is in effect, due to the electrical field, acting orthogonally in relation to the field lines 47, on the dielectrics that are in proximity of the electrical field. The dielectrics must be viewed as components of the fiber material 42. Subsequently, any and all components of the fiber material 42 are attracted by the electrical field. However, due to the fact that the fibers of the fiber material, meaning the long fibers, are retained by the conveying means (in the shown example, this is the clothing), only the impurities 46 and the short fibers are pulled into the electrical field.

In FIG. 3, the electrodes 43, 44 are disposed orthogonally in relation to the fiber material 42. In FIG. 4, on the other hand, the electrodes 43, 44 are disposed as inclined at an angle α in relation to the fiber material 42. If the fiber material 42 is viewed as extending in one plane, the field lines 47 of the electrical field between the electrodes 43, 44 are in a plane that has the same alignment relative to the surface of the plane constituted by the fiber material 42. This applies with regard to the configurations as shown in FIGS. 3 and 4, provided that an inclined position of the field lines 47 in relation to the surface of the fiber material 42 is considered as having the same alignment when an angle α is 60° or less. A position that is inclined by an angle α of below 60° results in the fact that the action of force 45, which occurs orthogonally in relation to the field lines 47, has a component having an orthogonal effect in relation to the fiber material 42 of theoretically half the size of the action of force 45. Experience has shown that an action of force acting on the impurities 46, which is reduced by half, results, if correspondingly high field strengths are present, in good cleaning results. If the angle α were more than 60°, the field lines 47 would no longer be the same but directed toward the surface of the fiber material 42.

FIG. 5 shows a schematic view of a representation of a third embodiment. The fiber material 42 is conveyed by a conveying means 40 in the direction of movement 41. A first electrode 50 and a second electrode 51 are disposed above the fiber material 42 at a spacing B. The electrodes 50 and 51 are directed toward each other at a spacing A, and they constitute a pair of electrodes. The electrodes 50, 51 are depicted as plates; they have cross-sections that decrease in parallel to the decreasing spacing in relation to the fiber material 42. The spacing A between the electrodes 50, 51 is greatest in relation to the fiber material 42 at the spacing B and continually decreases over the further course of the electrodes 50, 51. The electrodes 43, 44 are connected to a source of high voltage 48. This way, an electrical field is generated between the electrodes 43, 44, which is characterized in the representation by the field lines 47 and the field strength Ē. The field strength results from the quotient of the voltage that is applied by the source of high voltage and the spacing A of the electrodes 50, 51. Due to the geometrical shape of the electrodes 50, 51, the field strength Ē increases with the increase of the spacing in relation to the fiber material 42.

The action of force 45 that is in effect orthogonally in relation to the field lines 47 also increases with the increasing spacing of the fiber material 42, due to the changing field strength Ē. This causes the impurities 46 to be transported to the narrowest location between the electrodes 50, 51.

The field lines 47 enter and/or exit the electrodes 50, 51 perpendicularly in relation to the surfaces of the electrodes 50, 51. The result is an inhomogeneous field with slightly curved field lines 47 that are adjusted to the geometrical form of the electrodes 50 51. However, this is not relevant for the effect thereof. When the electrodes 50, 51 are disposed symmetrically, the action of force 45 is directed in the direction of the angle bisector from the angles of entry and exit of the field lines.

FIG. 6 is a schematic view of a representation of a fourth embodiment. In contrast to the configuration according to FIG. 5, the spacing A between electrodes 60, 61, which changes over the length of the electrodes 60, 61, is formed by the arrangement, and not the geometrical form, of the electrodes 60, 61. As shown in the representation in FIG. 6, it is not absolutely necessary for the electrodes 60, 61 to be disposed symmetrically. In this embodiment, the field lines 47 also enter and exit perpendicularly in and out of the electrodes 60, 61. As long as the electrodes 60, 61 are not disposed in an inclined position of more than 60° in relation to the surface of the fiber material 42, the field lines 47 must be viewed as running in a plane that extends in the same direction relative to the surface of the fiber material 42.

FIG. 7 shows a schematic view of a representation of a fifth embodiment. The pairs of electrodes as constituted by the electrodes 70, 71 correspond to the embodiment that was described in FIG. 5. The depicted embodiment of the electrodes 70, 71 has been selected arbitrarily. The fiber material 42 that is transported past the electrodes 70, 71 by a conveying means 40 includes a transport means, directed toward the observer of FIG. 7. The field lines 47 of the electrical field that is generated by the electrodes 70, 71 are, correspondingly, arranged at a right angle in relation to the conveying direction of the fiber material 42. It is immaterial as to whether the conveying direction of the fiber material 42 coincides with the alignment of the field lines 47. The action of force that is crucial for the cleaning action is orthogonal in relation to the field lines 47, whereby the alignment of the field lines 47 in relation to the conveying direction is not important. FIG. 7 shows a plurality of electrodes 70, 71 that are disposed offset in relation to each other at a spacing B above the fiber material 42. To improve the cleaning effect, it is advantageous to offset the pairs of electrodes, adjacently and behind to each other, (seen in the conveying direction of the fiber material). It is possible to connect a plurality of pairs of electrodes to the same source of high voltage 72.

LEGEND

-   1 Revolving flat -   2 Filling chute -   3 Taker-in -   4 Card cylinder -   5 Revolving flat set -   6 Deflection pulley -   7 Doffer -   8 Sliver-forming means -   9 Card sliver -   10 Revolving flat -   20 Cylinder clothing -   21 Flexible clothing -   22 Fiber material -   23 Direction of movement of the revolving card -   25 Direction of movement of the fiber material -   26 Parts of leaves -   27 Dust particles -   28 Parts of stems -   29 Parts of shells -   30 Fiber neps -   40 Conveying means -   41 Direction of movement -   42 Fiber material -   43, 44 Electrodes -   45 Action of force -   46 Impurities -   47 Field lines -   48 Source of high voltage -   50, 51 Electrodes -   60, 61 Electrodes -   70, 71 Electrodes -   72 Source of high voltage -   A Spacing between the electrodes of a pair of electrodes -   B Spacing between the electrode and fiber material -   Ē Field strength -   α Angle between the plane of the fiber material and the plane of the     field lines 

1. A device for separating dirt and short fibers from a fiber material (42) in a preparatory machine for a spinning apparatus, wherein the fiber material (42) that is made up of a plurality of fibers is retained by a conveying means (40), characterized in that the device comprises at least one pair of electrodes (43, 44, 50, 51, 60, 61, 70, 71), and in that the pair of electrodes (43, 44, 50, 51, 60, 61, 70, 71) is connected to a source of high voltage (48) for the purpose of generating an electrical field having a field strength (Ē), wherein the pair of electrodes (43, 44, 50, 51, 60, 61, 70, 71) is disposed as directed toward the fiber material (42), and in that the fiber material (42) is being moved in relation to the pair of electrodes (43, 44, 50, 51, 60, 61, 70, 71). 2-17. (canceled) 